Technical Field
The present application relates to a method and a device which, following the braking and positioning of a print sheet in a processing machine, is designed to activate, with the aid of at least one braking-force generating mechanism an additional transverse sheet brake that is connected to the operation of a downstream-arranged processing station.
The application thus refers to the production of folded print sheets in a folding apparatus, wherein the folding apparatus is typically equipped with a cross-folding device and/or a longitudinal folding device. The print sheets are typically processed starting with a paper roll, wherein this roll is first printed on in a printing press (digital or offset) and is then guided inline into the folding apparatus. Already printed paper rolls can also be supplied directly to the folding apparatus. The loose sheet in the form of a single sheet can furthermore be supplied via the printing press to the folding device, either printed or not printed.
For this, it must be ensured that the braking of the print sheet leads to a secure positioning before the print sheet can be supplied to the folding operation, thus showing an obvious interdependence between braking and positioning and folding operation.
Prior Art
The folding of the different substrates (papers), in particular the longitudinal folding, is especially challenging from a process-technical view since the print sheets coming from the feed device must be redirected with a sword by 90° and must be supplied to a pair of folding rollers. Before the sheet sections are supplied with the aid of the sword or other folding device to the folding roller pair, the sheet section, which typically arrives from a cross-folding device, must be slowed down within a very short time (a few milliseconds or fractions of milliseconds) from the feeding speed to a speed of 0. With the presently known longitudinal folding devices, this is achieved either with a sheet stop or a combination of a sheet stop and a brush.
The purpose of the brush is to brake and smooth the incoming sheet sections over the width of the brush. For the most part the sheet sections arrive in the longitudinal folding device with the folding edge in the lead (cross fold). However, non-folded (meaning without cross fold) sections can also be supplied to the longitudinal folding device.
The longitudinal folding process is basically prior art. The main problem with the print sheet deflection into the folding rollers is above all the stopping of the print sheets at the so-called sheet stop, wherein the complete delay energy is generated abruptly at the sheet stop. This leads to the print sheet being compressed in the region of the sheet end stop or, with rigid print sheets, it results in the conversion of a portion of the energy in the form of bouncing back of the print sheet.
The compressing of the print sheets can result in damage to the folding edge and thus to poor quality products, depending on the paper type and the speed. During the bouncing back, the print products can furthermore turn slightly as compared to the optimum geometric position. With the following insertion point for the folding sword, this results in slanted or parallel folds. To reduce or eliminate these negative effects, a great number of different measures have been proposed which represent components of the prior art.
For example, the braking brush or brushes are located in the region in front of the sheet stop and must respectively be adjusted to the product thickness. The disadvantage of this solution is that the braking brushes are subject to strong mechanical wear and the adjustment to the paper thickness is generally very involved. Also, the supplying upper belts can run only to the end of the print sheet section. A bouncing back is thus prevented or the product is again returned to the end stop. However, damage to the print sheet at the end stop is not prevented in this way. Also conceivable is a combination with the above solution. Additional known systems are actively controlled braking devices which slow down the print sheet at the end so that the print sheet only needs to align itself with the end stop.
A system for braking paper sheets is known from the German patent document DE 199 21 169 C2. With this system, the products are advantageously slowed and stopped at the back, so that they can be stretched and rest flat on the base, e.g. a folding table. The system has a compact and simple design with few components and is easy to control. According to the description, the system can be used as a sheet brake on folding tables, as a brake for slowing-down stations, or in front of the paddles of paddle wheels, so that the products can be processed further without damage. By means of a support, paper sheets are conveyed via transport belts that are not shown therein, for example to a folding table for printing presses. These paper sheets can be products cut from paper webs in transverse-cutting devices which can be non-folded, or single-folded, or multiple folded and can be gathered or non-gathered products. A carrier extending above the paper movement direction is attached to a frame. At the end facing away from the frame, an electromagnet is arranged on the carrier. An armature moves inside its coil body, preferably perpendicular to the movement direction and surface of the paper sheets. At the end directed toward the movement track, an armature is provided with a brake shoe with thereto attached brake lining. A spring element can be used to move the brake shoe with spring action, e.g. a leaf spring of resilient steel or plastic material, which is connected to the carrier through a receptacle. Also conceivable would be a screw spring which is directly accommodated by the armature and supports itself on the housing for the electromagnet, as well as on an armature indention. By electrically triggering the electromagnet, a magnetic flux field is generated, the force effect of which causes the armature to press the paper sheet via the brake shoe with lining against another brake lining that is fixedly attached to the support.
German patent document DE 43 07 383 A1 discloses a system for stopping sheets, in particular paper sheets. The sheets are successively transported to a braking system by a fast-moving series of belts, consisting of several spaced-apart, parallel-arranged lower belts and upper belts. While the discharge-side deflection rollers for the lower belts are positioned in front of the braking system, the upper belts extend further into the region of the braking system. The braking system consists of a guide metal extending over the working width, which is arranged below the intake plane. At a track discharge end of the sheet metal, a slot nozzle is arranged through which compressed air is blown counter to the sheet movement direction across the top of the guide sheet and is directed upward by the sheet end that is curved upward. The air flow generates a vacuum or low pressure which pulls the back edges of the sheets downward and simultaneously slows down the sheets. The air nozzle is followed directly by a circulating overlap blanket, having the width of the machine, which moves at a slower deposit speed. The sheets deflected downward by the airflow from the nozzle detach themselves from the upper belts and are deposited on the blanket. In the process, the front edge of the following, not yet decelerated sheet, slides over its back edge and an overlapping flow is created which is then transported further at a slower deposit speed.